alexc said:
Here's a link to an interesting paper by Bob Carver - covers the 'magnetic field effect' amp and tailored transfer functions
http://carvermk2.com/Docs/Carver%20Magnetic%20Field%20Whitepaper.pdf
Seems the magnetic thing was a triac circuit in the psu traffo primary.
Thanks I knew there was a reason I was blocking that out... Bob is a very clever guy but the marketing who hah in that "white paper" gives white papers a bad name.
As I suggested the amp uses multi-rail supply AKA Class H and invented by Hitachi IIRC. Using a light dimmer circuit on the transformer primary to scale for 2/4/8 ohm load seems clever, several amps would use different transformer windings.
The "Magnetic Amp" is more clever branding than descriptive of what is going on, but the amp did squeeze a bunch of music power from less iron/aluminum. For a while Clair Brothers, used these for serious sound reinforcement, but as Clair Brothers often do they modified the amps with bigger PS caps and IIRC replaced the power switch or something odd like that.
Bob is a good engineer and his appreciation for importance of transfer function is more important than this trick amplifier that burned across the consumer market like a meteor.
If I wasn't busy I would search out his patent, but trying to make sense of his ad-speak using a triac on the transformer primary as a "regulator" has limitations. Triacs are like the hotel califorina, you can turn them on, but you can't turn them off. You need to wait until the AC waveform returns to zero, so like a light dimmer, you adjust where you turn it on on the already falling waveform to get a lower voltage. Unfortunately if the music decides that it wants more voltage instantly, you need to wait until the next mains cycle , say 8mSec for FW rectified supply.
But a clever overall design, that I tend to under-appreciate because of the hyperbolic marketing. The scary part is I suspect Bob was involved in that too. He struck me as a little frustrated as he mastered the amplifier technology better (IMO) than effectively dominating the marketplace, while he did quite well for a time (several times).
JR
PS: on my list of related amplifier tricks, that I never got around to doing, and now never will because Class D makes them all moot, was an idea to add a similar back slope regulator on the secondary to vary just the lower intermediate PS rail of a class G/H amplifier. On the secondary side I could literally pull less voltage from the same single high voltage winding, delivering on the promise, Carver hinted at (crude power factor improvement). I used this variant synchronous rectification trick in my Loftech TS-1 power supply back in the '80s to pull a high current 5V supply from a 15V winding without wasting 2x the power as heat in a pass regulator. This amp low voltage/power rail could be regulated based on actual musical demand to make the amplifier very efficient by sizing it to match the music demand closely. The high rail is always sitting there charged up and ready to meet sudden transient needs. The low rail can be brought up higher in several mSec as needed so you don't give up all your efficiency running off the high voltage rail for more than a few Msec. A good idea for maybe a few decades ago, not so much now. :'(